Yeast is a live fungus that ferments sugar to produce alcohol and is widely used in the making of food products. There are different types of yeast that are suited for different purposes. Certain recipes require the right mix of yeast to achieve its optimal taste. Even though some types of yeast can be used for different purposes, if you tweak the recipe, others are so different that they don't work at all for them and causes issues with the taste, and might lead to stomach problems. It is essential to choose the type suited for your cooking.
Active Dry yeast
Active dry yeast needs to be dissolved in water before use for cooking. The yeast itself is in a hibernation state and is activated before use. This particular type of yeast should not be exposed to water of temperature higher than 43C as it might cause the yeast to die. These are generally sold in jars or ¼ ounce envelopes and should be refrigerated after opening the pack and using it. Generally, every yeast used to make bakery products are termed as Baker's yeast, and so it can be not very clear if such subcategories exist within the yeast family.
Caked yeast or Fresh yeast is sold in a compressed form. It should be used within a few weeks of purchase because this yeast degrades and dies off quickly. Once opened, it should be tested for potency before adding it as an ingredient to the recipe. The yeast is dissolved in warm water, and a pinch of sugar is added to check if it can perform fermentation or not. If it does not foam within five to ten minutes, then it is not fit for use. This process of checking is called yeast proofing.
Liquid and Instant yeast
Liquid yeast was popular in the 19th century before cake yeast was invented. It is actually a slurry of yeast and water. As long the solution is supplied with carbohydrates, the liquid yeast stays active. However, it is challenging to preserve or make it possible to transport them as the yeast might die without getting enough carbohydrates to live on. It was like the sourdough and bread starter. This form of yeast is not widely used these days.
Instant yeast is the most popular form of yeast, as it does not require dissolving in water before adding it to the recipes. It is very stable and comfortable with preserving and could be stored at room temperature in a tightly closed jar till the expiration date. It is also called rapid-rise yeast and bread yeast, and it is widely used in baking bread.